Homeostatic circuit for neural networks

ABSTRACT

A homeostatic circuit for neural networks includes a feedback circuit, a first electronic switch, a synapse circuit, a second electronic switch, a third electronic switch and a first capacitor. The feedback circuit is configured to receive the total synaptic driving current and output a feedback voltage which varies with the total synaptic driving current. The first electronic switch is connected with the synapse circuit and the second electronic switch and configured to receive the feedback voltage and output a current control signal according to the feedback voltage. The second electronic switch is connected with the synapse circuit and the third electronic switch and configured to output a first voltage signal according to the current control signal. The third electronic switch is configured to adjust the total synaptic driving current in a direction opposite to variation tendency of the total synaptic driving current according to the first voltage signal.

FIELD OF THE PATENT APPLICATION

The present patent application generally relates to medical electronicsand more specifically to a homeostatic circuit for neural networks.

BACKGROUND

The hardware implementation of a neural network system requires that acircuit should work against the drifts produced by the neural networksystem under the influence of certain external conditions. For example,when the temperature varies, the input of the system may vary. In orderto realize the stable operation of the neural network, the circuit musttake proper homeostatic actions to adapt to such variations and keep thesystem working around an operating point. A feature of theaforementioned variations is that the time scale is relatively long,which requires that the time period for the homeostatic actions of thecircuit should be relatively long. Otherwise, the homeostatic actionswill interfere with the signal processing or learning mechanism of theneural network.

Conventional homeostatic actions for neural networks are generallyrealized by floating gate transistors or software control and oftenrequire an external memory and a processor at the same time, which leadsto high power consumption, high cost and difficulty in realizinglarge-scale and high-density integration with other artificial neuralcomputing systems.

SUMMARY

The present patent application is directed to a homeostatic circuit forneural networks configured to keep a total synaptic driving current in apredetermined range around an optimal operating point. In one aspect,the homeostatic circuit for neural networks includes a feedback circuit;a first electronic switch; a synapse circuit; a second electronicswitch; a third electronic switch; a first capacitor; and a fourthelectronic switch. The feedback circuit is configured to receive thetotal synaptic driving current and output a feedback voltage whichvaries with the total synaptic driving current. The first electronicswitch is electrically connected with the synapse circuit and the secondelectronic switch and configured to receive the feedback voltage andoutput a current control signal according to the feedback voltage. Thegate electrode of the first electronic switch is electrically connectedwith the feedback circuit. The second electronic switch is electricallyconnected with the synapse circuit and the third electronic switch andconfigured to output a first voltage signal according to the currentcontrol signal. The drain electrode of the third electronic switch iselectrically connected with the feedback circuit. The third electronicswitch is configured to adjust the total synaptic driving current in adirection opposite to variation tendency of the total synaptic drivingcurrent according to the first voltage signal so as to keep the totalsynaptic driving current in the predetermined range. One end of thefirst capacitor is electrically connected with a power supply voltagewhile the other end of the first capacitor is electrically connectedwith the third electronic switch. The total synaptic driving current isproduced by the integrating effect of the homeostatic circuit for neuralnetworks through the first capacitor. The fourth electronic switch iselectrically connected with the second electronic switch and configuredto provide a constant current for the second electronic switch so thatvariation tendency of the first voltage signal is the same as variationtendency of the current control signal. The feedback circuit includes acomparator and a control voltage generator which are electricallyconnected with each other. The comparator includes a first input port, asecond input port and an output port. The first input port is configuredto receive a reference current, the second input port being configuredto receive the total synaptic driving current and the output port beingconfigured to output a second voltage signal. The control voltagegenerator is configured to receive the second voltage signal and producethe feedback voltage. The control voltage generator includes a fifthelectronic switch, a first voltage module, a second voltage module, athird voltage module and a second capacitor, the fifth electronic switchbeing electrically connected with the first voltage module, the secondvoltage module, the third voltage module and the second capacitor. Thefirst voltage module is configured to provide a first comparison voltagefor the fifth electronic switch. The second voltage module is configuredto provide a second comparison voltage for the fifth electronic switch.The third voltage module is configured to control conducting state ofthe fifth electronic switch. The second capacitor is configured tooutput the feedback voltage. When the first comparison voltage isgreater than the second comparison voltage, the second capacitor iscontrolled by the fifth electronic switch to be charged. When the firstcomparison voltage is lower than the second comparison voltage, thefifth electronic switch controls the second capacitor to be dischargedso as to control the feedback voltage to vary slowly.

The first electronic switch and the second electronic switch may beN-type Metal-Oxide Semiconductor Field Effect Transistors while thethird electronic switch, the fourth electronic switch and the fifthelectronic switch may be P-type Metal-Oxide Semiconductor Field EffectTransistors.

In another aspect, the present patent application provides a homeostaticcircuit for neural networks. The homeostatic circuit for neural networksincludes a feedback circuit; a first electronic switch; a synapsecircuit; a second electronic switch; a third electronic switch; and afirst capacitor. The feedback circuit is configured to receive the totalsynaptic driving current and output a feedback voltage varying with thetotal synaptic driving current. The first electronic switch iselectrically connected with the synapse circuit and the secondelectronic switch and configured to receive the feedback voltage andoutput a current control signal according to the feedback voltage. Thegate electrode of the first electronic switch is electrically connectedwith the feedback circuit. The second electronic switch is electricallyconnected with the synapse circuit and the third electronic switch andconfigured to output a first voltage signal according to the currentcontrol signal. The drain electrode of the third electronic switch iselectrically connected with the feedback circuit. The third electronicswitch is configured to adjust the total synaptic driving current in adirection opposite to variation tendency of the total synaptic drivingcurrent according to the first voltage signal so as to keep the totalsynaptic driving current in the predetermined range. One end of thefirst capacitor is electrically connected with a power supply voltagewhile the other end of the first capacitor is electrically connectedwith the third electronic switch. The total synaptic driving current isproduced by the integrating effect of the homeostatic circuit for neuralnetworks through the first capacitor.

Variation tendency of the feedback voltage, the current control signaland the first voltage signal may be the same as variation tendency ofthe total synaptic driving current. The homeostatic circuit for neuralnetworks may further include a fourth electronic switch. The fourthelectronic switch may be electrically connected with the secondelectronic switch and configured to provide a constant current for thesecond electronic switch so that variation tendency of the first voltagesignal may be the same as variation tendency of the current controlsignal.

The first electronic switch and the second electronic switch may beN-type Metal-Oxide Semiconductor Field Effect Transistors. The thirdelectronic switch and the fourth electronic switch may be P-typeMetal-Oxide Semiconductor Field Effect Transistors. The drain electrodeof the first electronic switch may be electrically connected with apower supply voltage, and the source electrode of the first electronicswitch may be electrically connected with the synapse circuit. The gateelectrode of the second electronic switch may be electrically connectedwith the gate electrode of the third electronic switch, the drainelectrode of the second electronic switch may be electrically connectedwith the drain electrode of the fourth electronic switch, and the sourceelectrode of the second electronic switch may be electrically connectedwith the synapse circuit. The source electrode of the third electronicswitch may be electrically connected with the power supply voltage. Thegate electrode of the fourth electronic switch may be electricallyconnected with a first biasing voltage and the source electrode of thefourth electronic switch may be electrically connected with the powersupply voltage.

The feedback circuit may include a comparator and a control voltagegenerator which may be electrically connected with each other. Thecomparator may include a first input port, a second input port and anoutput port. The first input port may be configured to receive areference current. The second input port may be configured to receivethe total synaptic driving current. The output port may be configured tooutput a second voltage signal. The control voltage generator may beconfigured to receive the second voltage signal and produce the feedbackvoltage.

The control voltage generator may include a fifth electronic switch, afirst voltage module, a second voltage module, a third voltage moduleand a second capacitor, the fifth electronic switch being electricallyconnected with the first voltage module, the second voltage module, thethird voltage module and the second capacitor. The first voltage modulemay be configured to provide a first comparison voltage for the fifthelectronic switch. The second voltage module may be configured toprovide a second comparison voltage for the fifth electronic switch. Thethird voltage module may be configured to control conducting state ofthe fifth electronic switch. The second capacitor may be configured tooutput the feedback voltage. When the first comparison voltage may begreater than the second comparison voltage, the second capacitor may becontrolled by the fifth electronic switch to be charged. When the firstcomparison voltage may be lower than the second comparison voltage, thefifth electronic switch may control the second capacitor to bedischarged so as to control the feedback voltage to vary slowly.

The first voltage module may include a sixth electronic switch, aseventh electronic switch, a first amplifier and an eighth electronicswitch. The second voltage module may include a second amplifier. Thethird voltage module may include a ninth electronic switch. The fifthelectronic switch, the sixth electronic switch, the eighth electronicswitch and the ninth electronic switch may be P-type Metal-OxideSemiconductor Field Effect Transistors. The seventh electronic switchmay be an N-type Metal-Oxide Semiconductor Field Effect Transistor. Thesource electrode of the fifth electronic switch may be electricallyconnected with the first voltage module. The drain electrode of thefifth electronic switch may be electrically connected with the secondvoltage module and the second capacitor. The gate electrode of the fifthelectronic switch may be electrically connected with the third voltagemodule. The gate electrode of the sixth electronic switch may receivethe second voltage signal. The source electrode of the sixth electronicswitch may receive a first predetermined voltage. The drain electrode ofthe sixth electronic switch may be electrically connected with thepositive input port of the first amplifier. The gate electrode of theseventh electronic switch may receive the second voltage signal. Thedrain electrode of the seventh electronic switch may receive a secondpredetermined voltage. The source electrode of the seventh electronicswitch may be electrically connected with the positive input port of thefirst amplifier. The negative input port of the first amplifier may beelectrically connected with the output port of the first amplifier andthe source electrode of the eighth electronic switch.

The gate electrode of the eighth electronic switch may receive a resetvoltage; the drain electrode of the eighth electronic switch may beelectrically connected with the source electrode of the fifth electronicswitch. The negative input port of the second amplifier may beelectrically connected with the drain electrode of the fifth electronicswitch; the positive input port of the second amplifier may receive areference voltage; the output port of the second amplifier may beelectrically connected with a port of the second capacitor which outputsthe feedback voltage. The gate electrode of the ninth electronic switchmay receive the reset voltage; the source electrode of the ninthelectronic switch may receive a second biasing voltage; the drainelectrode of the ninth electronic switch may be electrically connectedwith the gate electrode of the fifth electronic switch.

The control voltage generator may further include a reset module. Thereset module may be electrically connected with the second capacitor andconfigured to discharge the second capacitor completely so as to depletethe charges of the second capacitor and reset the second capacitor. Thereset module may include a tenth electronic switch and an eleventhelectronic switch. The tenth electronic switch may be an N-typeMetal-Oxide Semiconductor Field Effect Transistor while the eleventhelectronic switch may be a P-type Metal-Oxide Semiconductor Field EffectTransistor. The gate electrode of the tenth electronic switch mayreceive the reset voltage, the source electrode of the tenth electronicswitch may be connected to the ground, and the drain electrode of thetenth electronic switch may be electrically connected with the gateelectrode of the fifth electronic switch. The gate electrode of theeleventh electronic switch may receive a reversed voltage of the resetvoltage, the source electrode of the eleventh electronic switch may beelectrically connected with the source electrode of the fifth electronicswitch, the drain electrode of the eleventh electronic switch may beelectrically connected with a port of the second capacitor which outputsthe feedback voltage. When the tenth electronic switch and the eleventhelectronic switch may be conducted, the second capacitor may bedischarged. When discharging of the second capacitor may be finished,the tenth electronic switch and the eleventh electronic switch may bedisconnected.

In yet another aspect, the present patent application provides ahomeostatic circuit for neural networks. The homeostatic circuit forneural networks includes a feedback circuit; a first electronic switch;a synapse circuit; a second electronic switch; a third electronicswitch; and a first capacitor. The first electronic switch iselectrically connected with the synapse circuit and the secondelectronic switch and configured to receive the feedback voltage andoutput a current control signal according to the feedback voltage. Thegate electrode of the first electronic switch is electrically connectedwith the feedback circuit. The second electronic switch is electricallyconnected with the synapse circuit and the third electronic switch andconfigured to output a first voltage signal according to the currentcontrol signal. The drain electrode of the third electronic switch iselectrically connected with the feedback circuit. The third electronicswitch is configured to adjust the total synaptic driving current in adirection opposite to variation tendency of the total synaptic drivingcurrent according to the first voltage signal so as to keep the totalsynaptic driving current in the predetermined range.

One end of the first capacitor is electrically connected with a powersupply voltage while the other end of the first capacitor iselectrically connected with the third electronic switch.

The feedback circuit may be configured to receive the total synapticdriving current and output a feedback voltage varying with the totalsynaptic driving current. The total synaptic driving current may beproduced by the integrating effect of the homeostatic circuit for neuralnetworks through the first capacitor. Variation tendency of the feedbackvoltage, the current control signal and the first voltage signal may bethe same as variation tendency of the total synaptic driving current.

The homeostatic circuit for neural networks may further include a fourthelectronic switch. The fourth electronic switch may be electricallyconnected with the second electronic switch and configured to provide aconstant current for the second electronic switch so that variationtendency of the first voltage signal may be the same as variationtendency of the current control signal.

The first electronic switch and the second electronic switch may beN-type Metal-Oxide Semiconductor Field Effect Transistors. The thirdelectronic switch and the fourth electronic switch may be P-typeMetal-Oxide Semiconductor Field Effect Transistors. The drain electrodeof the first electronic switch may be electrically connected with apower supply voltage, and the source electrode of the first electronicswitch may be electrically connected with the synapse circuit. The gateelectrode of the second electronic switch may be electrically connectedwith the gate electrode of the third electronic switch, the drainelectrode of the second electronic switch may be electrically connectedwith the drain electrode of the fourth electronic switch, and the sourceelectrode of the second electronic switch may be electrically connectedwith the synapse circuit. The source electrode of the third electronicswitch may be electrically connected with the power supply voltage. Thegate electrode of the fourth electronic switch may be electricallyconnected with a first biasing voltage and the source electrode of thefourth electronic switch may be electrically connected with the powersupply voltage.

The feedback circuit may include a comparator and a control voltagegenerator which are electrically connected with each other. Thecomparator may include a first input port, a second input port and anoutput port. The first input port may be configured to receive areference current. The second input port may be configured to receivethe total synaptic driving current. The output port may be configured tooutput a second voltage signal. The control voltage generator may beconfigured to receive the second voltage signal and produce the feedbackvoltage.

The control voltage generator may include a fifth electronic switch, afirst voltage module, a second voltage module, a third voltage moduleand a second capacitor, the fifth electronic switch being electricallyconnected with the first voltage module, the second voltage module, thethird voltage module and the second capacitor. The first voltage modulemay be configured to provide a first comparison voltage for the fifthelectronic switch. The second voltage module may be configured toprovide a second comparison voltage for the fifth electronic switch. Thethird voltage module may be configured to control conducting state ofthe fifth electronic switch. The second capacitor may be configured tooutput the feedback voltage. When the first comparison voltage may begreater than the second comparison voltage, the second capacitor may becontrolled by the fifth electronic switch to be charged. When the firstcomparison voltage may be lower than the second comparison voltage, thefifth electronic switch may control the second capacitor to bedischarged so as to control the feedback voltage to vary slowly.

The first voltage module may include a sixth electronic switch, aseventh electronic switch, a first amplifier and an eighth electronicswitch. The second voltage module may include a second amplifier. Thethird voltage module may include a ninth electronic switch. The fifthelectronic switch, the sixth electronic switch, the eighth electronicswitch and the ninth electronic switch may be P-type Metal-OxideSemiconductor Field Effect Transistors. The seventh electronic switchmay be an N-type Metal-Oxide Semiconductor Field Effect Transistor. Thesource electrode of the fifth electronic switch may be electricallyconnected with the first voltage module. The drain electrode of thefifth electronic switch may be electrically connected with the secondvoltage module and the second capacitor. The gate electrode of the fifthelectronic switch may be electrically connected with the third voltagemodule. The gate electrode of the sixth electronic switch may receivethe second voltage signal. The source electrode of the sixth electronicswitch may receive a first predetermined voltage. The drain electrode ofthe sixth electronic switch may be electrically connected with thepositive input port of the first amplifier. The gate electrode of theseventh electronic switch may receive the second voltage signal. Thedrain electrode of the seventh electronic switch may receive a secondpredetermined voltage. The source electrode of the seventh electronicswitch may be electrically connected with the positive input port of thefirst amplifier. The negative input port of the first amplifier may beelectrically connected with the output port of the first amplifier andthe source electrode of the eighth electronic switch.

The gate electrode of the eighth electronic switch may receive a resetvoltage; the drain electrode of the eighth electronic switch may beelectrically connected with the source electrode of the fifth electronicswitch. The negative input port of the second amplifier may beelectrically connected with the drain electrode of the fifth electronicswitch; the positive input port of the second amplifier may receive areference voltage; the output port of the second amplifier may beelectrically connected with a port of the second capacitor which outputsthe feedback voltage. The gate electrode of the ninth electronic switchmay receive the reset voltage; the source electrode of the ninthelectronic switch may receive a second biasing voltage; the drainelectrode of the ninth electronic switch may be electrically connectedwith the gate electrode of the fifth electronic switch.

The control voltage generator may further include a reset module. Thereset module may be electrically connected with the second capacitor andconfigured to discharge the second capacitor completely so as to depletethe charges of the second capacitor and reset the second capacitor. Thereset module may include a tenth electronic switch and an eleventhelectronic switch. The tenth electronic switch may be an N-typeMetal-Oxide Semiconductor Field Effect Transistor while the eleventhelectronic switch may be a P-type Metal-Oxide Semiconductor Field EffectTransistor. The gate electrode of the tenth electronic switch mayreceive the reset voltage, the source electrode of the tenth electronicswitch may be connected to the ground, and the drain electrode of thetenth electronic switch may be electrically connected with the gateelectrode of the fifth electronic switch. The gate electrode of theeleventh electronic switch may receive a reversed voltage of the resetvoltage, the source electrode of the eleventh electronic switch may beelectrically connected with the source electrode of the fifth electronicswitch, the drain electrode of the eleventh electronic switch may beelectrically connected with a port of the second capacitor which outputsthe feedback voltage. When the tenth electronic switch and the eleventhelectronic switch may be conducted, the second capacitor may bedischarged. When discharging of the second capacitor may be finished,the tenth electronic switch and the eleventh electronic switch may bedisconnected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram of a homeostatic circuit forneural networks in accordance with an embodiment of the present patentapplication.

FIG. 2 is a schematic circuit diagram of a feedback circuit of thehomeostatic circuit for neural networks as depicted in FIG. 1 .

FIG. 3 is a block diagram of a control voltage generator of thehomeostatic circuit for neural networks as depicted in FIG. 1 .

FIG. 4 is a schematic circuit diagram of the control voltage generatoras depicted in FIG. 3 .

DETAILED DESCRIPTION

Reference will now be made in detail to a preferred embodiment of thehomeostatic circuit for neural networks disclosed in the present patentapplication, examples of which are also provided in the followingdescription. Exemplary embodiments of the homeostatic circuit for neuralnetworks disclosed in the present patent application are described indetail, although it will be apparent to those skilled in the relevantart that some features that are not particularly important to anunderstanding of the homeostatic circuit for neural networks may not beshown for the sake of clarity.

Furthermore, it should be understood that the homeostatic circuit forneural networks disclosed in the present patent application is notlimited to the precise embodiments described below and that variouschanges and modifications thereof may be effected by one skilled in theart without departing from the spirit or scope of the protection. Forexample, elements and/or features of different illustrative embodimentsmay be combined with each other and/or substituted for each other withinthe scope of this disclosure.

FIG. 1 is a schematic circuit diagram of a homeostatic circuit forneural networks in accordance with an embodiment of the present patentapplication. The homeostatic circuit 100 for neural networks isconfigured to keep a total synaptic driving current I0 in apredetermined range around an optimal operating point, while notaffecting the signal processing and learning mechanism of the neuralnetwork. Referring to FIG. 1 , the homeostatic circuit 100 for neuralnetworks includes a synapse circuit 101, a feedback circuit 20, a firstelectronic switch 11, a second electronic switch 12, a third electronicswitch 13 and a first capacitor CI.

The synapse circuit 101 is configured to receive a total weightedcurrent It for all synapses and split the total weighted current It intomultiple local currents, each local current corresponding to eachsynapse, so as to transmit the local currents to the correspondingsynapses respectively. The local current of each synapse varies with thesignal processing and learning mechanism of the neural network.

The feedback circuit 20 is configured to receive the total synapticdriving current I0 and output a feedback voltage Vx which varies withthe total synaptic driving current I0. The total synaptic drivingcurrent I0 represents the overall degree of activity of a neuron, whichhas global effects and varies with the external environment. Thevariation of the total synaptic driving current I0 is relativelyindependent from the variation of the input current It of the synapsecircuit 101.

The first electronic switch 11 is electronically connected with thesynapse circuit 101 and the second electronic switch 12 and configuredto receive the feedback voltage Vx and output a current control signalI1 according to the feedback voltage Vx. The second electronic switch 12is electrically connected with the synapse circuit 101 and the thirdelectronic switch 13 and configured to output a first voltage signal V0according to the current control signal I1. The third electronic switch13 is configured to adjust the total synaptic driving current I0 in adirection opposite to the variation tendency of the total synapticdriving current I0 according to the first voltage signal V0 so as tokeep the total synaptic driving current I0 in the predetermined range.One port of the first capacitor CI is electrically connected with apower supply voltage VDD while the other port of the first capacitor CIis electrically connected with the third electronic switch 13. The totalsynaptic driving current I0 is produced by the integrating effect of thehomeostatic circuit 100 for neural networks through the first capacitorCI and eventually directed to a neural network circuit (not shown in thefigures) so that a neuron signal is produced based on the total synapticdriving current I0.

In this embodiment, the variation tendencies of the feedback voltage Vx,the current control signal I1 and the first voltage signal V0 are thesame as that of the total synaptic driving current I0.

The homeostatic circuit 100 for neural networks further includes afourth electronic switch 14. The fourth electronic switch 14 iselectrically connected with the second electronic switch 12 andconfigured to provide a constant current for the second electronicswitch 12, so that the variation tendency of the first voltage signal V0is the same as that of the current control signal I1.

In this embodiment, the first electronic switch 11 and the secondelectronic switch 12 are N-type Metal-Oxide Semiconductor Field EffectTransistors while the third electronic switch 13 and the fourthelectronic switch 14 are P-type Metal-Oxide Semiconductor Field EffectTransistors, each including a gate electrode, a drain electrode and asource electrode.

The gate electrode of the first electronic switch 11 is electricallyconnected with the feedback circuit 20, the drain electrode of the firstelectronic switch 11 being electrically connected with a power supplyvoltage VDD, and the source electrode of the first electronic switch 11being electrically connected with the synapse circuit 101. The gateelectrode of the second electronic switch 12 is electrically connectedwith the gate electrode of the third electronic switch 13, the drainelectrode of the second electronic switch 12 being electricallyconnected with the drain electrode of the fourth electronic switch 14and the source electrode of the second electronic switch 12 beingelectrically connected with the synapse circuit 101. The drain electrodeof the third electronic switch 13 is electrically connected with thefeedback circuit 20 while the source electrode of the third electronicswitch 13 is electrically connected with the power supply voltage VDD.The gate electrode of the fourth electronic switch 14 is electricallyconnected with a first biasing voltage VB1 while the source electrode ofthe fourth electronic switch 14 is electrically connected with the powersupply voltage VDD.

The working principle of the homeostatic circuit 100 for neural networksis as follows: when the total synaptic driving current I0 increases andI0 is greater than a reference current IR, the feedback voltage Vxproduced by the feedback circuit 20 increases so that I0 decreases(suppressing the increase of I0 and reducing I0 to IR); when the totalsynaptic driving current I0 decreases and I0 is lower than the referencecurrent IR, the feedback voltage Vx produced by the feedback circuit 20decreases so that I0 increases (suppressing the decrease of I0 andincreasing I0 to IR). The aforementioned process is slow and takes arelatively long time to finish.

In order to make it convenient to describe the working process,reference points a, b, d, e and f are referred to in the homeostaticcircuit 100 for neural networks, wherein the reference point a is set atthe gate electrode of the first electronic switch 11, the referencepoint b being set at the source electrode of the first electronic switch11, the reference point d being set at the gate electrode of the fourthelectronic switch 14, the reference point e being set at the gateelectrode of the second electronic switch 12, and the reference point fbeing set at the gate electrode of the third electronic switch 13.

Specifically, when the total synaptic driving current I0 increases, thefeedback voltage Vx increases. As a result, Va increases and Ibincreases. Since the voltage VB1 of the reference point d is constant,the voltage difference VDD-VB1 between the source electrode and the gateelectrode of the fourth electronic switch 14 is constant, so that thecurrent flowing through the fourth electronic switch 14 to the secondelectronic switch 12 is constant. Therefore, when Ib increases, Ieinevitably increases, and therefore the first voltage signal V0increases which leads to the increase of Vf. As a result, the voltagedifference VDD-Vf between the source electrode and the gate electrode ofthe third electronic switch 13 decreases, which reduces the current I0flowing through the drain electrode of the third electronic switch 13 tothe reference current IR. And vice versa, when the total synapticdriving current I0 decreases, the feedback voltage Vx decreases andtherefore Va and Ib decrease which leads to the decrease of Ie. As aresult, the first voltage signal V0 decreases which leads to thedecrease of Vf and therefore VDD-Vf increases, which increases thecurrent I0 flowing through the drain electrode of the third electronicswitch 13 to the reference current IR.

Referring to FIG. 2 , the feedback circuit 20 includes a comparator 21and a control voltage generator 30 which are electrically connected witheach other.

The comparator 21 includes a first input port 21 a, a second input port21 b and an output port 21 c. The first input port 21 a is configured toreceive the reference current IR and the second input port 21 b isconfigured to receive the total synaptic driving current I0 and theoutput port 21 c is configured to output a second voltage signal Vc.

The working principle of the feedback circuit 20 is: when I0 is greaterthan IR, Vc=1 and the feedback voltage Vx increases; when I0 is lowerthan IR, Vc=0 and the feedback voltage Vx decreases.

Referring to FIG. 3 , the control voltage generator 30 is configured toreceive the second voltage signal Vc and produce the feedback voltageVx. The control voltage generator 30 includes a fifth electronic switch15, a first voltage module 31, a second voltage module 32, a thirdvoltage module 33 and a second capacitor C0. The fifth electronic switch15 is electrically connected with the first voltage module 31, thesecond voltage module 32, the third voltage module 33 and the secondcapacitor C0.

The first voltage module 31 is configured to provide a first comparisonvoltage V3 for the fifth electronic switch 15. The second voltage module32 is configured to provide a second comparison voltage V4 for the fifthelectronic switch 15. The third voltage module 33 is configured tocontrol the conducting state of the fifth electronic switch 15. Thesecond capacitor C0 is configured to output the feedback voltage Vx.When the first comparison voltage V3 is greater than the secondcomparison voltage V4, the second capacitor C0 is controlled by thefifth electronic switch 15 to be charged. When the first comparisonvoltage V3 is lower than the second comparison voltage V4, the fifthelectronic switch 15 controls the second capacitor C0 to be dischargedso as to control the feedback voltage Vx to vary slowly.

Referring to FIG. 4 , the first voltage module 31 includes a sixthelectronic switch 16, a seventh electronic switch 17, a first amplifier311 and an eighth electronic switch 18. The second voltage module 32includes a second amplifier 321. The third voltage module 33 includes aninth electronic switch 19.

In this embodiment, the fifth electronic switch 15, the sixth electronicswitch 16, the eighth electronic switch 18 and the ninth electronicswitch 19 are P-type Metal-Oxide Semiconductor Field Effect Transistorswhile the seventh electronic switch 17 is an N-type Metal-OxideSemiconductor Field Effect Transistor.

The source electrode of the fifth electronic switch 15 is electricallyconnected with the first voltage module 31, the drain electrode of thefifth electronic switch 15 being electrically connected with the secondvoltage module 32 and the second capacitor C0, and the gate electrode ofthe fifth electronic switch 15 being electrically connected with thethird voltage module 33. The gate electrode of the sixth electronicswitch 16 receives the second voltage signal Vc, the source electrode ofthe sixth electronic switch 16 receives a first predetermined voltageV1, and the drain electrode of the sixth electronic switch 16 iselectrically connected with the positive input port of the firstamplifier 311. The gate electrode of the seventh electronic switch 17receives the second voltage signal Vc, the drain electrode of theseventh electronic switch 17 receives a second predetermined voltage V2,and the source electrode of the seventh electronic switch 17 iselectrically connected with the positive input port of the firstamplifier 311. The negative input port of the first amplifier 311 iselectrically connected with the output port of the first amplifier 311and the source electrode of the eighth electronic switch 18. The gateelectrode of the eighth electronic switch 18 receives a reset voltage VSwhile the drain electrode of the eighth electronic switch 18 iselectrically connected with the source electrode of the fifth electronicswitch 15. The negative input port of the second amplifier 321 iselectrically connected with the drain electrode of the fifth electronicswitch 15, the positive input port of the second amplifier 321 receivesa reference voltage VR, and the output port of the second amplifier 321is electrically connected with one port of the second capacitor C0 whichoutputs the feedback voltage Vx. The gate electrode of the ninthelectronic switch 19 receives the reset voltage VS, the source electrodeof the ninth electronic switch 19 receives a second biasing voltage VB2,and the drain electrode of the ninth electronic switch 19 iselectrically connected with the gate electrode of the fifth electronicswitch 15.

In addition, referring to FIG. 3 , the control voltage generator 30further includes a reset module 34. The reset module 34 is electricallyconnected with the second capacitor C0 and configured to discharge thesecond capacitor C0 completely so as to deplete the charges of thesecond capacitor C0 and reset the second capacitor C0.

Referring to FIG. 4 , the reset module 34 includes a tenth electronicswitch 110 and an eleventh electronic switch 111.

In this embodiment, the tenth electronic switch 110 is an N-typeMetal-Oxide Semiconductor Field Effect Transistor and the eleventhelectronic switch 111 is a P-type Metal-Oxide Semiconductor Field EffectTransistor.

The gate electrode of the tenth electronic switch 110 receives the resetvoltage VS, the source electrode of the tenth electronic switch 110 isconnected to the ground, and the drain electrode of the tenth electronicswitch 110 is electrically connected with the gate electrode of thefifth electronic switch 15. The gate electrode of the eleventhelectronic switch 111 receives a reversed voltage VS of the resetvoltage, the source electrode of the eleventh electronic switch 111 iselectrically connected with the source electrode of the fifth electronicswitch 15, and the drain electrode of the eleventh electronic switch 111is electrically connected with one port of the second capacitor C0 whichoutputs the feedback voltage Vx.

The working principle of the reset module 34 is: controlling theconducting state of the tenth electronic switch 110 and the eleventhelectronic switch 111 through controlling the reset voltage VS.Specifically, when the homeostatic circuit 100 for neural networksresets, the tenth electronic switch 110 and the eleventh electronicswitch 111 are conducted so that the second capacitor C0 is discharged.When discharging of the second capacitor C0 is finished, the homeostaticcircuit 100 for neural networks finishes resetting, and the tenthelectronic switch 110 and the eleventh electronic switch 111 aredisconnected.

To make it convenient to describe, the positive input port of the firstamplifier 311 is referred to as a reference point k and the sourceelectrode of the eighth electronic switch 18 is referred to as areference point h.

The working process of the control voltage generator 30 is:predetermining the values of the first predetermined voltage V1, thesecond predetermined voltage V2 and the reference voltage VR so thatV1>VR>V2. At the very beginning, the reset voltage VS=1 while VS=0. Thetenth electronic switch 110 and the eleventh electronic switch 111 areconducted while the ninth electronic switch 19 is disconnected, so thatthe gate electrode of the fifth electronic switch 15 is directlyconnected to the ground and therefore having an electric potential ofzero. The fifth electronic switch 15 is conducted so that V3=V4. Thesecond capacitor C0 is discharged and when the second capacitor C0 isdischarged completely and reset, the reset voltage VS=0. Since VS=0,VS=1 so that the eleventh electronic switch 111 is disconnected. At thesame time, since the voltages of the gate electrode of the tenthelectronic switch 110 and the gate electrode of the ninth electronicswitch 19 are VS, after being reset, the tenth electronic switch 110 isdisconnected and the ninth electronic switch 19 is conducted, so thatthe biasing voltage VB2 of the source electrode of the ninth electronicswitch 19 is transmitted to the gate electrode of the fifth electronicswitch 15 and VG=VB2.

(1) When Vc=1, the sixth electronic switch 16 is disconnected and theseventh electronic switch 17 is conducted, so that Vk=V2. Since thereset voltage VS=0, the eighth electronic switch 18 is conducted andV3=Vh. Under the first amplifier 311 (when the magnification of thefirst amplifier 311 is very large), V1≈Vh, and in other words, V3≈V2. Atthe same time, under the second amplifier 321 (when the magnification ofthe second amplifier 321 is very large), V4≈VR. Since the second biasingvoltage VB2 received by the source electrode of the ninth electronicswitch 19 is transmitted to the gate electrode of the fifth electronicswitch 15, VG=VB2. For the fifth electronic switch 15, the voltagedifference between the drain electrode and the source electrodeVDS=VD−VS=V4−V3=VR−V2>0. In other words, the voltage VD of the drainelectrode of the fifth electronic switch 15 is greater than the voltageVS of the source electrode of the fifth electronic switch 15 while thecurrent flows from the drain electrode to the source electrode. Sincethe eleventh electronic switch 111 is disconnected, the second capacitorC0 is discharged slowly and the feedback voltage Vx increases slowly.

(2) When VC=0, the sixth electronic switch 16 is conducted and theseventh electronic switch 17 is disconnected, so that Vk=V1. Since thereset voltage VS=0, the eighth electronic switch 18 is conducted andV3=Vh. Under the first amplifier 311, V1≈Vh, and in other words, V3≈V1.At the same time, under the second amplifier 321, V4≈VR. Since thesecond biasing voltage VB2 received by the source electrode of the ninthelectronic switch 19 is transmitted to the gate electrode of the fifthelectronic switch 15, VG=VB2. For the fifth electronic switch 15, thevoltage difference between the drain electrode and the source electrodeVDS=VD−VS=V4−V3=VR−V2<0. In other words, the voltage VD of the drainelectrode of the fifth electronic switch 15 is lower than the voltage VSof the source electrode of the fifth electronic switch 15 while thecurrent flows from the source electrode to the drain electrode. Sincethe eleventh electronic switch 111 is disconnected, the second capacitorC0 is charged slowly and the feedback voltage Vx increases slowly.

From what is mentioned above, the control voltage generator 30accurately adjusts the flowing direction of the current between thesource electrode and the drain electrode of the fifth electronic switch15 so as to charge or discharge the second capacitor C0 slowly for along time, and accurately adjusts the intensity of the current betweenthe source electrode and the drain electrode of the fifth electronicswitch 15 so as to control the time period for charging and dischargingthe second capacitor C0. Therefore, in the present patent application,the second biasing voltage VB2 is adjusted to a very small value (i.e.slightly lower than the conducting threshold of the fifth electronicswitch 15 which is called “sub threshold” for short), so that the valueof the current IDS between the source electrode and the drain electrodeof the fifth electronic switch 15 is adjusted to a very small one so asto effectively lengthen the time period for charging and discharging.

Furthermore, the size of a chip in a large-scale integrated neuron isvery small, so it requires that the capacitance should be very small(e.g. the capacitance of the second capacitor C0 is 1-10 pF) and thecurrent should be very small. The homeostatic circuit 100 for neuralnetworks can accurately adjust the current IDS between the drainelectrode and the source electrode of the fifth electronic switch 15 toa very small value by predetermining the values of V1, V2, VR and VB2,and charge and discharge the second capacitor C0 slowly through IDS soas to lengthen the adjusting time of the homeostatic circuit 100 forneural networks to several hours.

Furthermore, the voltage VDS between the drain electrode and the sourceelectrode of the fifth electronic switch 15 is very small, so it helpsto reduce the diffusion of minority carriers.

Furthermore, the fifth electronic switch 15 further includes a bulkelectrode and the bulk electrode receives the reference voltage VR. Thereference voltage of the bulk electrode of the fifth electronic switch15 is VR and the voltage of the drain electrode of the fifth electronicswitch 15 is V4. Under the second amplifier 321, V4≈VR so that thecurrent IDB between the drain electrode and the bulk electrode of thefifth electronic switch 15 is approximately 0, and in other words, thecurrent between the drain electrode and the bulk electrode of the fifthelectronic switch 15 is effectively eliminated and the impact of thecurrent IDB between the drain electrode and the bulk electrode on thecurrent IDS between the drain electrode and the source electrode isreduced so that the accuracy of IDS is effectively controlled.

Furthermore, the oxide layer thickness of the gate electrode of thefifth electronic switch 15 is about 5 nm and the voltage VDG between thegate electrode and the drain electrode of the fifth electronic switch 15is about 0.5V, so that the density of the leakage current of the gateelectrode of the fifth electronic switch 15 is about 10⁻⁸ A/m² while theleakage current between the gate electrode and the drain electrode ofthe fifth electronic switch 15 is effectively reduced.

In other words, in the present patent application, the undesired leakagecurrent of the fifth electronic switch 15 (i.e. leakage current betweenthe bulk electrode and the drain electrode and leakage current betweenthe gate electrode and the drain electrode) is eliminated as much aspossible and only wanted current is retained (i.e. the current IDSbetween the source electrode and the drain electrode), so that thecharging and discharging current IDS and the time period for chargingand discharging can be accurately controlled.

Compared with the conventional homeostatic circuits for neural networks,in the present patent application, the current of the homeostaticcircuit for neural networks is very small, so the power consumption isvery low. Besides, the homeostatic circuit for neural networks can beimplemented with common electronic components with low cost. At the sametime, the current is very small, so the capacitance is very low and thesize of the chip is very small, which helps to realize large-scale andhigh density integration with other artificial neural computing systems.

While the present patent application has been shown and described withparticular references to a number of embodiments thereof, it should benoted that various other changes or modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A homeostatic circuit for neural networksconfigured to keep a total synaptic driving current in a predeterminedrange around an optimal operating point, the homeostatic circuit forneural networks comprising: a feedback circuit; a first electronicswitch; a synapse circuit; a second electronic switch; a thirdelectronic switch; a first capacitor; and a fourth electronic switch;wherein: the feedback circuit is configured to receive the totalsynaptic driving current and output a feedback voltage which varies withthe total synaptic driving current; the first electronic switch iselectrically connected with the synapse circuit and the secondelectronic switch and configured to receive the feedback voltage andoutput a current control signal according to the feedback voltage; thegate electrode of the first electronic switch is electrically connectedwith the feedback circuit; the second electronic switch is electricallyconnected with the synapse circuit and the third electronic switch andconfigured to output a first voltage signal according to the currentcontrol signal; the drain electrode of the third electronic switch iselectrically connected with the feedback circuit; the third electronicswitch is configured to adjust the total synaptic driving current in adirection opposite to variation tendency of the total synaptic drivingcurrent according to the first voltage signal so as to keep the totalsynaptic driving current in the predetermined range; one end of thefirst capacitor is electrically connected with a power supply voltagewhile the other end of the first capacitor is electrically connectedwith the third electronic switch; the total synaptic driving current isproduced by the integrating effect of the homeostatic circuit for neuralnetworks through the first capacitor; the fourth electronic switch iselectrically connected with the second electronic switch and configuredto provide a constant current for the second electronic switch so thatvariation tendency of the first voltage signal is the same as variationtendency of the current control signal; the feedback circuit comprises acomparator and a control voltage generator which are electricallyconnected with each other; the comparator comprises a first input port,a second input port and an output port; the first input port isconfigured to receive a reference current, the second input port beingconfigured to receive the total synaptic driving current and the outputport being configured to output a second voltage signal; the controlvoltage generator is configured to receive the second voltage signal andproduce the feedback voltage; the control voltage generator comprises afifth electronic switch, a first voltage module, a second voltagemodule, a third voltage module and a second capacitor, the fifthelectronic switch being electrically connected with the first voltagemodule, the second voltage module, the third voltage module and thesecond capacitor; the first voltage module is configured to provide afirst comparison voltage for the fifth electronic switch; the secondvoltage module is configured to provide a second comparison voltage forthe fifth electronic switch; the third voltage module is configured tocontrol conducting state of the fifth electronic switch; the secondcapacitor is configured to output the feedback voltage; when the firstcomparison voltage is greater than the second comparison voltage, thesecond capacitor is controlled by the fifth electronic switch to becharged; and when the first comparison voltage is lower than the secondcomparison voltage, the fifth electronic switch controls the secondcapacitor to be discharged so as to control the feedback voltage to varyslowly.
 2. The homeostatic circuit for neural networks of claim 1,wherein the first electronic switch and the second electronic switch areN-type Metal-Oxide Semiconductor Field Effect Transistors while thethird electronic switch, the fourth electronic switch and the fifthelectronic switch are P-type Metal-Oxide Semiconductor Field EffectTransistors.
 3. A homeostatic circuit for neural networks configured tokeep a total synaptic driving current in a predetermined range around anoptimal operating point, the homeostatic circuit for neural networkscomprising: a feedback circuit; a first electronic switch; a synapsecircuit; a second electronic switch; a third electronic switch; and afirst capacitor; wherein: the feedback circuit is configured to receivethe total synaptic driving current and output a feedback voltage varyingwith the total synaptic driving current; the first electronic switch iselectrically connected with the synapse circuit and the secondelectronic switch and configured to receive the feedback voltage andoutput a current control signal according to the feedback voltage; thegate electrode of the first electronic switch is electrically connectedwith the feedback circuit; the second electronic switch is electricallyconnected with the synapse circuit and the third electronic switch andconfigured to output a first voltage signal according to the currentcontrol signal; the drain electrode of the third electronic switch iselectrically connected with the feedback circuit; the third electronicswitch is configured to adjust the total synaptic driving current in adirection opposite to variation tendency of the total synaptic drivingcurrent according to the first voltage signal so as to keep the totalsynaptic driving current in the predetermined range; one end of thefirst capacitor is electrically connected with a power supply voltagewhile the other end of the first capacitor is electrically connectedwith the third electronic switch; and the total synaptic driving currentis produced by the integrating effect of the homeostatic circuit forneural networks through the first capacitor.
 4. The homeostatic circuitfor neural networks of claim 3, wherein variation tendency of thefeedback voltage, the current control signal and the first voltagesignal is the same as variation tendency of the total synaptic drivingcurrent.
 5. The homeostatic circuit for neural networks of claim 4further comprising a fourth electronic switch, wherein the fourthelectronic switch is electrically connected with the second electronicswitch and configured to provide a constant current for the secondelectronic switch so that variation tendency of the first voltage signalis the same as variation tendency of the current control signal.
 6. Thehomeostatic circuit for neural networks of claim 5, wherein the firstelectronic switch and the second electronic switch are N-typeMetal-Oxide Semiconductor Field Effect Transistors; the third electronicswitch and the fourth electronic switch are P-type Metal-OxideSemiconductor Field Effect Transistors; the drain electrode of the firstelectronic switch is electrically connected with a power supply voltage,and the source electrode of the first electronic switch is electricallyconnected with the synapse circuit; the gate electrode of the secondelectronic switch is electrically connected with the gate electrode ofthe third electronic switch, the drain electrode of the secondelectronic switch being electrically connected with the drain electrodeof the fourth electronic switch, and the source electrode of the secondelectronic switch being electrically connected with the synapse circuit;the source electrode of the third electronic switch is electricallyconnected with the power supply voltage; the gate electrode of thefourth electronic switch is electrically connected with a first biasingvoltage and the source electrode of the fourth electronic switch iselectrically connected with the power supply voltage.
 7. The homeostaticcircuit for neural networks of claim 6, wherein the feedback circuitcomprises a comparator and a control voltage generator which areelectrically connected with each other; the comparator comprises a firstinput port, a second input port and an output port; the first input portis configured to receive a reference current; the second input port isconfigured to receive the total synaptic driving current; the outputport is configured to output a second voltage signal; the controlvoltage generator is configured to receive the second voltage signal andproduce the feedback voltage.
 8. The homeostatic circuit for neuralnetworks of claim 7, wherein the control voltage generator comprises afifth electronic switch, a first voltage module, a second voltagemodule, a third voltage module and a second capacitor, the fifthelectronic switch being electrically connected with the first voltagemodule, the second voltage module, the third voltage module and thesecond capacitor; the first voltage module is configured to provide afirst comparison voltage for the fifth electronic switch; the secondvoltage module is configured to provide a second comparison voltage forthe fifth electronic switch; the third voltage module is configured tocontrol conducting state of the fifth electronic switch; the secondcapacitor is configured to output the feedback voltage; when the firstcomparison voltage is greater than the second comparison voltage, thesecond capacitor is controlled by the fifth electronic switch to becharged; when the first comparison voltage is lower than the secondcomparison voltage, the fifth electronic switch controls the secondcapacitor to be discharged so as to control the feedback voltage to varyslowly.
 9. The homeostatic circuit for neural networks of claim 8,wherein the first voltage module comprises a sixth electronic switch, aseventh electronic switch, a first amplifier and an eighth electronicswitch; the second voltage module comprises a second amplifier; thethird voltage module comprises a ninth electronic switch; the fifthelectronic switch, the sixth electronic switch, the eighth electronicswitch and the ninth electronic switch are P-type Metal-OxideSemiconductor Field Effect Transistors; the seventh electronic switch isan N-type Metal-Oxide Semiconductor Field Effect Transistor; the sourceelectrode of the fifth electronic switch is electrically connected withthe first voltage module; the drain electrode of the fifth electronicswitch is electrically connected with the second voltage module and thesecond capacitor; the gate electrode of the fifth electronic switch iselectrically connected with the third voltage module; the gate electrodeof the sixth electronic switch receives the second voltage signal; thesource electrode of the sixth electronic switch receives a firstpredetermined voltage; the drain electrode of the sixth electronicswitch is electrically connected with the positive input port of thefirst amplifier; the gate electrode of the seventh electronic switchreceives the second voltage signal; the drain electrode of the seventhelectronic switch receives a second predetermined voltage; the sourceelectrode of the seventh electronic switch is electrically connectedwith the positive input port of the first amplifier; the negative inputport of the first amplifier is electrically connected with the outputport of the first amplifier and the source electrode of the eighthelectronic switch; the gate electrode of the eighth electronic switchreceives a reset voltage; the drain electrode of the eighth electronicswitch is electrically connected with the source electrode of the fifthelectronic switch; the negative input port of the second amplifier iselectrically connected with the drain electrode of the fifth electronicswitch; the positive input port of the second amplifier receives areference voltage; the output port of the second amplifier iselectrically connected with a port of the second capacitor which outputsthe feedback voltage; the gate electrode of the ninth electronic switchreceives the reset voltage; the source electrode of the ninth electronicswitch receives a second biasing voltage; the drain electrode of theninth electronic switch is electrically connected with the gateelectrode of the fifth electronic switch.
 10. The homeostatic circuitfor neural networks of claim 9, wherein the control voltage generatorfurther comprises a reset module; the reset module is electricallyconnected with the second capacitor and configured to discharge thesecond capacitor completely so as to deplete the charges of the secondcapacitor and reset the second capacitor; the reset module comprises atenth electronic switch and an eleventh electronic switch; the tenthelectronic switch is an N-type Metal-Oxide Semiconductor Field EffectTransistor while the eleventh electronic switch is a P-type Metal-OxideSemiconductor Field Effect Transistor; the gate electrode of the tenthelectronic switch receives the reset voltage, the source electrode ofthe tenth electronic switch being connected to the ground, and the drainelectrode of the tenth electronic switch being electrically connectedwith the gate electrode of the fifth electronic switch; the gateelectrode of the eleventh electronic switch receives a reversed voltageof the reset voltage, the source electrode of the eleventh electronicswitch being electrically connected with the source electrode of thefifth electronic switch, the drain electrode of the eleventh electronicswitch being electrically connected with a port of the second capacitorwhich outputs the feedback voltage; when the tenth electronic switch andthe eleventh electronic switch are conducted, the second capacitor isdischarged; when discharging of the second capacitor is finished, thetenth electronic switch and the eleventh electronic switch aredisconnected.
 11. A homeostatic circuit for neural networks configuredto keep a total synaptic driving current in a predetermined range aroundan optimal operating point, the homeostatic circuit for neural networkscomprising: a feedback circuit; a first electronic switch; a synapsecircuit; a second electronic switch; a third electronic switch; and afirst capacitor; wherein: the first electronic switch is electricallyconnected with the synapse circuit and the second electronic switch andconfigured to receive the feedback voltage and output a current controlsignal according to the feedback voltage; the gate electrode of thefirst electronic switch is electrically connected with the feedbackcircuit; the second electronic switch is electrically connected with thesynapse circuit and the third electronic switch and configured to outputa first voltage signal according to the current control signal; thedrain electrode of the third electronic switch is electrically connectedwith the feedback circuit; the third electronic switch is configured toadjust the total synaptic driving current in a direction opposite tovariation tendency of the total synaptic driving current according tothe first voltage signal so as to keep the total synaptic drivingcurrent in the predetermined range; and one end of the first capacitoris electrically connected with a power supply voltage while the otherend of the first capacitor is electrically connected with the thirdelectronic switch.
 12. The homeostatic circuit for neural networks ofclaim 11, wherein the feedback circuit is configured to receive thetotal synaptic driving current and output a feedback voltage varyingwith the total synaptic driving current.
 13. The homeostatic circuit forneural networks of claim 11, wherein the total synaptic driving currentis produced by the integrating effect of the homeostatic circuit forneural networks through the first capacitor.
 14. The homeostatic circuitfor neural networks of claim 12, wherein variation tendency of thefeedback voltage, the current control signal and the first voltagesignal is the same as variation tendency of the total synaptic drivingcurrent.
 15. The homeostatic circuit for neural networks of claim 14further comprising a fourth electronic switch, wherein the fourthelectronic switch is electrically connected with the second electronicswitch and configured to provide a constant current for the secondelectronic switch so that variation tendency of the first voltage signalis the same as variation tendency of the current control signal.
 16. Thehomeostatic circuit for neural networks of claim 15, wherein the firstelectronic switch and the second electronic switch are N-typeMetal-Oxide Semiconductor Field Effect Transistors; the third electronicswitch and the fourth electronic switch are P-type Metal-OxideSemiconductor Field Effect Transistors; the drain electrode of the firstelectronic switch is electrically connected with a power supply voltage,and the source electrode of the first electronic switch is electricallyconnected with the synapse circuit; the gate electrode of the secondelectronic switch is electrically connected with the gate electrode ofthe third electronic switch, the drain electrode of the secondelectronic switch being electrically connected with the drain electrodeof the fourth electronic switch, and the source electrode of the secondelectronic switch being electrically connected with the synapse circuit;the source electrode of the third electronic switch is electricallyconnected with the power supply voltage; the gate electrode of thefourth electronic switch is electrically connected with a first biasingvoltage and the source electrode of the fourth electronic switch iselectrically connected with the power supply voltage.
 17. Thehomeostatic circuit for neural networks of claim 16, wherein thefeedback circuit comprises a comparator and a control voltage generatorwhich are electrically connected with each other; the comparatorcomprises a first input port, a second input port and an output port;the first input port is configured to receive a reference current; thesecond input port is configured to receive the total synaptic drivingcurrent; the output port is configured to output a second voltagesignal; the control voltage generator is configured to receive thesecond voltage signal and produce the feedback voltage.
 18. Thehomeostatic circuit for neural networks of claim 17, wherein the controlvoltage generator comprises a fifth electronic switch, a first voltagemodule, a second voltage module, a third voltage module and a secondcapacitor, the fifth electronic switch being electrically connected withthe first voltage module, the second voltage module, the third voltagemodule and the second capacitor; the first voltage module is configuredto provide a first comparison voltage for the fifth electronic switch;the second voltage module is configured to provide a second comparisonvoltage for the fifth electronic switch; the third voltage module isconfigured to control conducting state of the fifth electronic switch;the second capacitor is configured to output the feedback voltage; whenthe first comparison voltage is greater than the second comparisonvoltage, the second capacitor is controlled by the fifth electronicswitch to be charged; when the first comparison voltage is lower thanthe second comparison voltage, the fifth electronic switch controls thesecond capacitor to be discharged so as to control the feedback voltageto vary slowly.
 19. The homeostatic circuit for neural networks of claim18, wherein the first voltage module comprises a sixth electronicswitch, a seventh electronic switch, a first amplifier and an eighthelectronic switch; the second voltage module comprises a secondamplifier; the third voltage module comprises a ninth electronic switch;the fifth electronic switch, the sixth electronic switch, the eighthelectronic switch and the ninth electronic switch are P-type Metal-OxideSemiconductor Field Effect Transistors; the seventh electronic switch isan N-type Metal-Oxide Semiconductor Field Effect Transistor; the sourceelectrode of the fifth electronic switch is electrically connected withthe first voltage module; the drain electrode of the fifth electronicswitch is electrically connected with the second voltage module and thesecond capacitor; the gate electrode of the fifth electronic switch iselectrically connected with the third voltage module; the gate electrodeof the sixth electronic switch receives the second voltage signal; thesource electrode of the sixth electronic switch receives a firstpredetermined voltage; the drain electrode of the sixth electronicswitch is electrically connected with the positive input port of thefirst amplifier; the gate electrode of the seventh electronic switchreceives the second voltage signal; the drain electrode of the seventhelectronic switch receives a second predetermined voltage; the sourceelectrode of the seventh electronic switch is electrically connectedwith the positive input port of the first amplifier; the negative inputport of the first amplifier is electrically connected with the outputport of the first amplifier and the source electrode of the eighthelectronic switch; the gate electrode of the eighth electronic switchreceives a reset voltage; the drain electrode of the eighth electronicswitch is electrically connected with the source electrode of the fifthelectronic switch; the negative input port of the second amplifier iselectrically connected with the drain electrode of the fifth electronicswitch; the positive input port of the second amplifier receives areference voltage; the output port of the second amplifier iselectrically connected with a port of the second capacitor which outputsthe feedback voltage; the gate electrode of the ninth electronic switchreceives the reset voltage; the source electrode of the ninth electronicswitch receives a second biasing voltage; the drain electrode of theninth electronic switch is electrically connected with the gateelectrode of the fifth electronic switch.
 20. The homeostatic circuitfor neural networks of claim 19, wherein the control voltage generatorfurther comprises a reset module; the reset module is electricallyconnected with the second capacitor and configured to discharge thesecond capacitor completely so as to deplete the charges of the secondcapacitor and reset the second capacitor; the reset module comprises atenth electronic switch and an eleventh electronic switch; the tenthelectronic switch is an N-type Metal-Oxide Semiconductor Field EffectTransistor while the eleventh electronic switch is a P-type Metal-OxideSemiconductor Field Effect Transistor; the gate electrode of the tenthelectronic switch receives the reset voltage, the source electrode ofthe tenth electronic switch being connected to the ground, and the drainelectrode of the tenth electronic switch being electrically connectedwith the gate electrode of the fifth electronic switch; the gateelectrode of the eleventh electronic switch receives a reversed voltageof the reset voltage, the source electrode of the eleventh electronicswitch being electrically connected with the source electrode of thefifth electronic switch, the drain electrode of the eleventh electronicswitch being electrically connected with a port of the second capacitorwhich outputs the feedback voltage; when the tenth electronic switch andthe eleventh electronic switch are conducted, the second capacitor isdischarged; when discharging of the second capacitor is finished, thetenth electronic switch and the eleventh electronic switch aredisconnected.